Human periodontal disease has been shown to be of bacterial etiology with host responses to periodontopathic bacteria, an essential contributing factor to progress of the sesion. A newly classified genus of Gram negative bacteria, the Capnocytophaga, has been associated with this disease. These organisms produce a poorly defined exopolysaccharide slime layer (EP) which may contribute of their pathogenicity. Since human periodontal disease is thought to involve host responses to bacterial products which may penetrate gingival tissue, knowledge of the chemical and immunologicl properties of the EP derived from the Capnocytophaga may aid in our understanding of the disease process. In this investigation, the EP from C. sputigena, C. gingivalis, and C. ochracea will be extracted from culture supernatants by ethanol precipitation and purified by gel filtration and ion exchange chromatography. Chemical analyses for protein, sugars, amino acids, nucleic acids, and endotoxin will be performed. The immunomodulatory potential of EP will be evaluated by examining their effect on the in vitro murine lymphocyte response to the T lymphocyte mitogen concanavalin A and the B lymphocyte mitogen lipopolysaccharide. The effect of EP on antibody formation in vivo will be examined using mice immunized with sheep erythrocytes by evaluating the numbers of antibody forming cells produced using the hemolytic plaque assay. The specific site(s) of EP immunomodulation will be identified by in vitro immunization experiments using purified populations of T cells, B cells, and macrophages. Binding of EP to these cells will be determined by indirect immunofluorescence. The fact that EP mau enhance or suppress immune responses to unrelated antigens may aid in explanation of the predominance of B lymphocytes and plasma cells in the periodontal disease is a polyclonal B cell response possibly caused by a hyperactive B cell state in the diseased patient. If EP were found to modulate the immune response (as other oral bacterial products such as teichoic acid and dextran do) this could explain the proposed altered immuno-reactivity, as well as the association of Capnocytophaga with this disease.